Surveys for Object Detection and Debris Clearance

Objects and debris on the seabed can cause damage to vessel intakes and dredging plant that can be avoided by a detailed hydrographic survey.

Hydrographic surveys can identify objects, such as wreckage, debris, or obstructions. An object is defined as any item on the seabed which is distinctly different from the surrounding area. It can be anything from an isolated rock to a wreck or abandoned construction material.

If hydrographic information and data are not correctly collected, analysed, and processed, objects may not be identified resulting in serious implications.

PHS use survey vessels equipped with specialised survey equipment and acoustic instrumentation for the detection and visualisation of underwater objects. Our pool of equipment includes multibeam echo sounders, side scan sonars, sub-bottom profilers, and magnetometers, which are well suited to detecting seabed objects.

What are MBES and SSS and how are they used for object detection and debris clearance?

PHS use Multibeam Echo Sounders (MBES) which emit soundwaves in a fan-like shape to map the seabed. Modern systems can detect objects less than 0.5m in size, and can define narrow pipes, cables, and ropes. It is common to run two MBES passes to confirm or disprove an object, this is done to eliminate the possibility of erroneous data, such as the detection of fish making their way through to the final data, resulting in a false representation of the available depth.

Side Scan Sonar (SSS) can also be used to detect objects by providing a clear sonar image of the seabed, objects are represented by the acoustic shadow cast from the low incident angle of the acoustic pulse on the seabed.

When SSS and MBES systems are used together they provide complementary findings and increase the validity of the obtained survey results.

Factors to consider when choosing which system to use include:

  • The objectives of the survey
  • The nature of the seabed
  • Scale or extent of work to be done
  • The minimum requirements for the project
  • The cost of procuring the technique

Why is object detection and debris clearance important?

Objects and debris can impact many marine infrastructure activities from dredging to offshore installation activities. Detection of objects and debris can assist in avoiding incidents with shipping and fouling of dredging and construction equipment.

Investment in extensive survey data collection may appear to be costly, but in the long term quality surveys are worthwhile. Generally, the value of hydrographic services is understated and is beyond the obvious benefit of improved nautical charts.

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We operate from offices in Adelaide, Karratha and Port Hedland.

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